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Macropore-Stabilized Limestone Sorbents Prepared by the Simultaneous Hydration–Impregnation Method for High-Temperature CO2 Capture

Xu, Yongqing, Luo, Cong, Zheng, Ying, Ding, Haoran, Zhang, Liqi
Energy & Fuels 2016 v.30 no.4 pp. 3219-3226
calcium, calcium oxide, carbon dioxide, carbonation, cost effectiveness, limestone, macropores, microstructure, sorbents, sorption, strength (mechanics)
A novel cost-effective method was applied to modified calcium-based sorbents for cyclic high-temperature CO₂ capture. The sorbents were derived from cheap limestone and sea salt, and the main processes of the preparation involved two simple steps: hydration of CaO and impregnation with sea salt in CaO. Results indicated that the simultaneous hydration–impregnation (SHI) method contributed to the formation of highly improved calcium-based sorbents during cyclic calcination/carbonation reactions. After 40 cycles, the SHI limestone doped with 3.0 wt % sea salt achieved a CO₂ capture capacity of 0.31 g of CO₂/g of sorbent, which was 126% higher than that of natural limestone. Moreover, the SHI limestone sorbent contained numerous macropores after several cycles. Further investigation on microstructure changes of the sorbents showed that the macropores were relatively stable during cyclic reactions, which can be attributed to the stable behavior of the sorbent. In contrast, the natural limestone lost its micro- and macropores during initial reactions, thereby rapidly losing its sorption capacity during calcium looping cycles. Furthermore, the SHI limestone sorbents showed slightly better mechanical strength than the natural limestone sorbent demonstrated by attrition tests.